In Daubert v. Merrell Dow Pharmaceuticals, Inc., 509
U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), this Court focused upon
the admissibility of scientific expert testimony. It pointed out
that such testimony is admissible only if it is both relevant and reliable.
And it held that the Federal Rules of Evidence "assign to the trial
judge the task of ensuring that an expert's testimony both rests
on a reliable foundation and is relevant to the task at hand." Id.,
at 597, 113 S.Ct. 2786. The Court also discussed certain more specific
factors, such as testing, peer review, error rates, and "acceptability"
in the relevant scientific community, some or all of which might prove
helpful in determining the reliability of a particular scientific "theory
or technique." Id., at 593-594, 113 S.Ct. 2786.

This case requires us to decide how Daubert applies to
the testimony of engineers and other experts who are not scientists.
We conclude that Daubert's general holding--setting forth the trial judge's
general "gatekeeping" obligation--applies not only to testimony
based on "scientific" knowledge, but also to testimony based
on "technical" and "other specialized" knowledge.
See Fed. Rule Evid. 702. We also conclude that a trial court may consider
one or more of the more specific factors that Daubert mentioned when doing
so will help determine that testimony's reliability. But, as the Court
stated in Daubert, the test of reliability is "flexible," and
Daubert's list of specific factors neither necessarily nor exclusively
applies to all experts or in every case. Rather, the law grants
a district court the same broad latitude when it decides how to determine
reliability as it enjoys in respect to its ultimate reliability determination.
See General Electric Co. v. Joiner, 522 U.S. 136, 143, 118 S.Ct. 512,
139 L.Ed.2d 508 (1997) (courts of appeals are to apply "abuse of
discretion" standard when reviewing district court's reliability
determination). Applying these standards, we determine that the District
Court's decision in this case--not to admit certain expert testimony--was
within its discretion and therefore lawful.

I

On July 6, 1993, the right rear tire of a minivan driven
by Patrick Carmichael blew out. In the accident that followed, one of
the passengers died, and others were severely injured. In October 1993,
the Carmichaels brought this diversity suit against the tire's maker and
its distributor, whom we refer to collectively as Kumho Tire, claiming
that the tire was defective. The plaintiffs rested their case in significant
part upon deposition testimony provided by an expert in tire failure
analysis, Dennis Carlson, Jr., who intended to testify in support of their
conclusion.

Carlson's depositions relied upon certain features of
tire technology that are not in dispute. A steel-belted radial tire like
the Carmichaels' is made up of a "carcass" containing many layers
of flexible cords, called "plies," along which (between the
cords and the outer tread) are laid steel strips called "belts."
Steel wire loops, called "beads," hold the cords together at
the plies' bottom edges. An outer layer, called the "tread,"
encases the carcass, and the entire tire is bound together in rubber,
through the application of heat and various chemicals. See generally,
e.g., J. Dixon, Tires, Suspension and Handling 68-72 (2d ed.1996). The
bead of the tire sits upon a "bead seat," which is part of the
wheel assembly. That assembly contains a "rim flange," which
extends over the bead and rests against the side of the tire. See M. Mavrigian,
Performance Wheels & Tires 81, 83 (1998) (illustrations).

Carlson's testimony also accepted certain background
facts about the tire in question. He assumed that before the blowout the
tire

TABULAR OR GRAPHIC MATERIAL SET AT THIS POINT IS NOT
DISPLAYABLE

*1172 had traveled far. (The tire was made in
1988 and had been installed some time before the Carmichaels bought the
used minivan in March 1993; the Carmichaels had driven the van approximately
7,000 additional miles in the two months they had owned it.) Carlson noted
that the tire's tread depth, which was 11/32 of an inch when new, App.
242, had been worn down to depths that ranged from 3/32 of an inch along
some parts of the tire, to nothing at all along others. Id., at 287. He
conceded that the tire tread had at least two punctures which had been
inadequately repaired. Id., at 258-261, 322.

Despite the tire's age and history, Carlson concluded
that a defect in its manufacture or design caused the blow-out. He rested
this conclusion in part upon three premises which, for present purposes,
we must assume are not in dispute: First, a tire's carcass should stay
bound to the inner side of the tread for a significant period of time
after its tread depth has worn away. Id., at 208-209. Second, the tread
of the tire at issue had separated from its inner steel-belted carcass
prior to the accident. Id., at 336. Third, this "separation"
caused the blowout. Ibid.

Carlson's conclusion that a defect caused the separation,
however, rested upon certain other propositions, several of which the
defendants strongly dispute. First, Carlson said that if a separation
is not caused by a certain kind of tire misuse called "overdeflection"
(which consists of underinflating the tire or causing it to carry too
much weight, thereby generating heat that can undo the chemical tread/carcass
bond), then, ordinarily, its cause is a tire defect. Id., at 193-195,
277-278. Second, he said that if a tire has been subject to sufficient
overdeflection to cause a separation, it should reveal certain physical
symptoms. These symptoms include (a) tread wear on the tire's shoulder
that is greater than the tread wear along the tire's center, id., at 211;
(b) signs of a "bead groove," where the beads have been pushed
too hard against the bead seat on the inside of the tire's rim, id., at
196- 197; (c) sidewalls of the tire with physical signs of deterioration,
such as discoloration, id., at 212; and/or (d) marks on the tire's rim
flange, id., at 219-220. Third, Carlson said that where he does not find
at least two of the four physical signs just mentioned (and presumably
where there is no reason to suspect a less common cause of separation),
he concludes that a manufacturing or design defect caused the separation.
Id., at 223-224.

Carlson added that he had inspected the tire in question.
He conceded that the tire to a limited degree showed greater wear on
*1173 the shoulder than in the center, some signs of "bead groove,"
some discoloration, a few marks on the rim flange, and inadequately filled
puncture holes (which can also cause heat that might lead to separation).
Id., at 256-257, 258-261, 277, 303-304, 308. But, in each instance, he
testified that the symptoms were not significant, and he explained why
he believed that they did not reveal overdeflection. For example, the
extra shoulder wear, he said, appeared primarily on one shoulder, whereas
an overdeflected tire would reveal equally abnormal wear on both shoulders.
Id., at 277. Carlson concluded that the tire did not bear at least two
of the four overdeflection symptoms, nor was there any less obvious cause
of separation; and since neither overdeflection nor the punctures caused
the blowout, a defect must have done so.

Kumho Tire moved the District Court to exclude Carlson's
testimony on the ground that his methodology failed Rule 702's reliability
requirement. The court agreed with Kumho that it should act as a Daubert-type
reliability "gatekeeper," even though one might consider Carlson's
testimony as "technical," rather than "scientific."
See Carmichael v. Samyang Tires, Inc., 923 F.Supp. 1514, 1521-1522 (S.D.Ala.1996).
The court then examined Carlson's methodology in light of the reliability-related
factors that Daubert mentioned, such as a theory's testability, whether
it "has been a subject of peer review or publication," the "known
or potential rate of error," and the "degree of acceptance ...
within the relevant scientific community." 923 F.Supp., at 1520 (citing
Daubert, 509 U.S., at 592-594, 113 S.Ct. 2786). The District Court found
that all those factors argued against the reliability of Carlson's methods,
and it granted the motion to exclude the testimony (as well as the defendants'
accompanying motion for summary judgment).

The plaintiffs, arguing that the court's application
of the Daubert factors was too "inflexible," asked for reconsideration.
And the Court granted that motion. Carmichael v. Samyang Tires, Inc.,
Civ. Action No. 93-0860-CB-S (S.D.Ala., June 5, 1996), App. to Pet. for
Cert. 1c. After reconsidering the matter, the court agreed with the plaintiffs
that Daubert should be applied flexibly, that its four factors were simply
illustrative, and that other factors could argue in favor of admissibility.
It conceded that there may be widespread acceptance of a "visual-inspection
method" for some relevant purposes. But the court found insufficient
indications of the reliability of

"the component of Carlson's tire failure analysis
which most concerned the Court, namely, the methodology employed by
the expert in analyzing the data obtained in the visual inspection,
and the scientific basis, if any, for such an analysis." Id., at
6c.

It consequently affirmed its earlier order declaring
Carlson's testimony inadmissable and granting the defendants' motion for
summary judgment.

The Eleventh Circuit reversed. See Carmichael v. Samyang
Tire, Inc., 131 F.3d 1433 (1997). It "review[ed] ... de novo "
the "district court's legal decision to apply Daubert." Id.,
at 1435. It noted that "the Supreme Court in Daubert explicitly limited
its holding to cover only the 'scientific context,' " adding that
"a Daubert analysis" applies only where an expert relies
"on the application of scientific principles," rather than "on
skill- or experience-based observation." Id., at 1435-1436. It concluded
that Carlson's testimony, which it viewed as relying on experience, "falls
outside the scope of Daubert," that "the district court erred
as a matter of law by applying Daubert in this case," and that the
case must be remanded for further (non-Daubert-type) consideration under
Rule 702. Id., at 1436.

[1] In Daubert, this Court held that Federal Rule of
Evidence 702 imposes a special obligation upon a trial judge to "ensure
that any and all scientific testimony ... is not only relevant, but reliable."
509 U.S., at 589, 113 S.Ct. 2786. The initial question before us is whether
this basic gatekeeping obligation applies only to "scientific"
testimony or to all expert testimony. We, like the parties, believe
that it applies to all expert testimony. See Brief for Petitioners
19; Brief for Respondents 17.

For one thing, Rule 702 itself says:

"If scientific, technical, or other specialized
knowledge will assist the trier of fact to understand the evidence or
to determine a fact in issue, a witness qualified as an expert by
knowledge, skill, experience, training, or education, may testify thereto
in the form of an opinion or otherwise."

This language makes no relevant distinction between "scientific"
knowledge and "technical" or "other specialized" knowledge.
It makes clear that any such knowledge might become the subject of expert
testimony. In Daubert, the Court specified that it is the Rule's word
"knowledge," not the words (like "scientific") that
modify that word, that "establishes a standard of evidentiary reliability."
509 U.S., at 589-590, 113 S.Ct. 2786. Hence, as a matter of language,
the Rule applies its reliability standard to all "scientific,"
"technical," or "other specialized" matters within
its scope. We concede that the Court in Daubert referred only to "scientific"
knowledge. But as the Court there said, it referred to "scientific"
testimony "because that [wa]s the nature of the expertise" at
issue. Id., at 590, n. 8, 113 S.Ct. 2786.

Neither is the evidentiary rationale that underlay the
Court's basic Daubert "gatekeeping" determination limited to
"scientific" knowledge. Daubert pointed out that Federal Rules
702 and 703 grant expert witnesses testimonial latitude unavailable
to other witnesses on the "assumption that the expert's opinion
will have a reliable basis in the knowledge and experience of his discipline."
Id., at 592, 113 S.Ct. 2786 (pointing out that experts may testify
to opinions, including those that are not based on firsthand knowledge
or observation). The Rules grant that latitude to all experts, not
just to "scientific" ones.

Finally, it would prove difficult, if not impossible,
for judges to administer evidentiary rules under which a gatekeeping obligation
depended upon a distinction between "scientific" knowledge and
"technical" or "other specialized" knowledge. There
is no clear line that divides the one from the others. Disciplines such
as engineering rest upon scientific knowledge. Pure scientific theory
itself may depend for its development upon observation and properly engineered
machinery. And conceptual efforts to distinguish the two are unlikely
to produce clear legal lines capable of application in particular cases.
Cf. Brief for National Academy of Engineering as Amicus Curiae 9 (scientist
seeks to understand nature while the engineer seeks nature's modification);
Brief for Rubber Manufacturers Association as Amicus Curiae 14- 16 (engineering,
as an "applied science," relies on "scientific reasoning
and methodology"); Brief for John Allen et al. as Amici Curiae 6
(engineering relies upon "scientific knowledge and methods").

Neither is there a convincing need to make such distinctions.
Experts of all kinds tie observations to conclusions through the
use of what Judge Learned Hand called "general truths derived from
... specialized experience." Hand, Historical and Practical Considerations
Regarding Expert Testimony, 15 Harv. L.Rev. 40, 54 (1901). And
whether the specific expert testimony focuses upon specialized
observations, the specialized translation of those observations into theory,
a specialized theory itself, or the application of such a theory in a
particular case, the expert's testimony often will rest "upon
an experience confessedly foreign in kind to [the jury's] own." Ibid.
The trial judge's effort to assure that the specialized testimony is reliable
and relevant can help the jury evaluate *1175 that foreign experience,
whether the testimony reflects scientific, technical, or other specialized
knowledge.

We conclude that Daubert's general principles apply to
the expert matters described in Rule 702. The Rule, in respect
to all such matters, "establishes a standard of evidentiary reliability."
509 U.S., at 590, 113 S.Ct. 2786. It "requires a valid ... connection
to the pertinent inquiry as a precondition to admissibility." Id.,
at 592, 113 S.Ct. 2786. And where such testimony's factual basis, data,
principles, methods, or their application are called sufficiently into
question, see Part III, infra, the trial judge must determine whether
the testimony has "a reliable basis in the knowledge and experience
of [the relevant] discipline." 509 U.S., at 592, 113 S.Ct. 2786.

B

The petitioners ask more specifically whether a trial
judge determining the "admissibility of an engineering expert's
testimony" may consider several more specific factors that Daubert
said might "bear on" a judge's gate-keeping determination. These
factors include:

--Whether a "theory or technique ... can be (and
has been) tested";

--Whether it "has been subjected to peer review
and publication";

--Whether, in respect to a particular technique, there
is a high "known or potential rate of error" and whether there
are "standards controlling the technique's operation"; and

Emphasizing the word "may" in the question,
we answer that question yes.

[2] Engineering testimony rests upon scientific foundations,
the reliability of which will be at issue in some cases. See, e.g., Brief
for Stephen Bobo et al. as Amici Curiae 23 (stressing the scientific bases
of engineering disciplines). In other cases, the relevant reliability
concerns may focus upon personal knowledge or experience. As the Solicitor
General points out, there are many different kinds of experts, and
many different kinds of expertise. See Brief for United States as Amicus
Curiae 18-19, and n. 5 (citing cases involving experts in drug
terms, handwriting analysis, criminal modus operandi, land valuation,
agricultural practices, railroad procedures, attorney's fee valuation,
and others). Our emphasis on the word "may" thus reflects Daubert's
description of the Rule 702 inquiry as "a flexible one." 509
U.S., at 594, 113 S.Ct. 2786. Daubert makes clear that the factors it
mentions do not constitute a "definitive checklist or test."
Id., at 593, 113 S.Ct. 2786. And Daubert adds that the gatekeeping inquiry
must be " 'tied to the facts' " of a particular "case."
Id., at 591, 113 S.Ct. 2786 (quoting United States v. Downing, 753 F.2d
1224, 1242 (C.A.3 1985)). We agree with the Solicitor General that "[t]he
factors identified in Daubert may or may not be pertinent in assessing
reliability, depending on the nature of the issue, the expert's particular
expertise, and the subject of his testimony." Brief for United States
as Amicus Curiae 19. The conclusion, in our view, is that we can neither
rule out, nor rule in, for all cases and for all time the applicability
of the factors mentioned in Daubert, nor can we now do so for subsets
of cases categorized by category of expert or by kind of evidence.
Too much depends upon the particular circumstances of the particular case
at issue.

Daubert itself is not to the contrary. It made clear
that its list of factors was meant to be helpful, not definitive. Indeed,
those factors do not all necessarily apply even in every instance in which
the reliability of scientific testimony is challenged. It might not be
surprising in a particular case, for example, that a claim made by a scientific
witness has never been the subject of peer review, for the particular
application at issue may never previously have interested any scientist.
Nor, on the other hand, does the presence of Daubert's general acceptance
factor help show that an expert's testimony is reliable where the
discipline itself lacks reliability, as, for example, do theories grounded
in any so-called generally accepted principles of astrology or necromancy.

*1176 At the same time, and contrary to the Court
of Appeals' view, some of Daubert's questions can help to evaluate the
reliability even of experience-based testimony. In certain cases, it will
be appropriate for the trial judge to ask, for example, how often an engineering
expert's experience- based methodology has produced erroneous results,
or whether such a method is generally accepted in the relevant engineering
community. Likewise, it will at times be useful to ask even of a witness
whose expertise is based purely on experience, say, a perfume tester able
to distinguish among 140 odors at a sniff, whether his preparation is
of a kind that others in the field would recognize as acceptable.

We must therefore disagree with the Eleventh Circuit's
holding that a trial judge may ask questions of the sort Daubert mentioned
only where an expert "relies on the application of scientific
principles," but not where an expert relies "on skill-
or experience-based observation." 131 F.3d, at 1435. We do not believe
that Rule 702 creates a schematism that segregates expertise by type while
mapping certain kinds of questions to certain kinds of experts. Life and
the legal cases that it generates are too complex to warrant so definitive
a match.

[3][4] To say this is not to deny the importance of Daubert's
gatekeeping requirement. The objective of that requirement is to ensure
the reliability and relevancy of expert testimony. It is to make
certain that an expert, whether basing testimony upon professional
studies or personal experience, employs in the courtroom the same level
of intellectual rigor that characterizes the practice of an expert
in the relevant field. Nor do we deny that, as stated in Daubert,
the particular questions that it mentioned will often be appropriate for
use in determining the reliability of challenged expert testimony.
Rather, we conclude that the trial judge must have considerable leeway
in deciding in a particular case how to go about determining whether particular
expert testimony is reliable. That is to say, a trial court should
consider the specific factors identified in Daubert where they are reasonable
measures of the reliability of expert testimony.

C

[5][6] The trial court must have the same kind of latitude
in deciding how to test an expert's reliability, and to decide
whether or when special briefing or other proceedings are needed to investigate
reliability, as it enjoys when it decides whether or not that expert's
relevant testimony is reliable. Our opinion in Joiner makes clear
that a court of appeals is to apply an abuse-of-discretion standard when
it "review[s] a trial court's decision to admit or exclude expert
testimony." 522 U.S., at 138-139, 118 S.Ct. 512. That standard
applies as much to the trial court's decisions about how to determine
reliability as to its ultimate conclusion. Otherwise, the trial judge
would lack the discretionary authority needed both to avoid unnecessary
"reliability" proceedings in ordinary cases where the reliability
of an expert's methods is properly taken for granted, and to require
appropriate proceedings in the less usual or more complex cases where
cause for questioning the expert's reliability arises. Indeed,
the Rules seek to avoid "unjustifiable expense and delay" as
part of their search for "truth" and the "jus[t] determin[ation]"
of proceedings. Fed. Rule Evid. 102. Thus, whether Daubert's specific
factors are, or are not, reasonable measures of reliability in a particular
case is a matter that the law grants the trial judge broad latitude to
determine. See Joiner, supra, at 143, 118 S.Ct. 512. And the Eleventh
Circuit erred insofar as it held to the contrary.

III

[7] We further explain the way in which a trial judge
"may" consider Daubert's factors by applying these considerations
to the case at hand, a matter that has been briefed exhaustively by the
parties and their 19 amici. The District Court did not doubt Carlson's
qualifications, which included a masters degree in mechanical engineering,
10 years' work at Michelin America, Inc., and testimony as a tire failure
consultant in other tort cases. Rather, it excluded the testimony because,
despite those qualifications, it initially *1177 doubted, and then
found unreliable, "the methodology employed by the expert in
analyzing the data obtained in the visual inspection, and the scientific
basis, if any, for such an analysis." Civ. Action No. 93-0860-CB-S
(S.D.Ala., June 5, 1996), App. to Pet. for Cert. 6c. After examining the
transcript in "some detail," 923 F.Supp., at 1518-519, n. 4,
and after considering respondents' defense of Carlson's methodology, the
District Court determined that Carlson's testimony was not reliable. It
fell outside the range where experts might reasonably differ, and
where the jury must decide among the conflicting views of different experts,
even though the evidence is "shaky." Daubert, 509 U.S.,
at 596, 113 S.Ct. 2786. In our view, the doubts that triggered the District
Court's initial inquiry here were reasonable, as was the court's ultimate
conclusion.

For one thing, and contrary to respondents' suggestion,
the specific issue before the court was not the reasonableness in general
of a tire expert's use of a visual and tactile inspection to determine
whether overdeflection had caused the tire's tread to separate from its
steel-belted carcass. Rather, it was the reasonableness of using such
an approach, along with Carlson's particular method of analyzing the data
thereby obtained, to draw a conclusion regarding the particular matter
to which the expert testimony was directly relevant. That matter
concerned the likelihood that a defect in the tire at issue caused its
tread to separate from its carcass. The tire in question, the expert
conceded, had traveled far enough so that some of the tread had been
worn bald; it should have been taken out of service; it had been repaired
(inadequately) for punctures; and it bore some of the very marks that
the expert said indicated, not a defect, but abuse through overdeflection.
See supra, at 1172; App. 293-294. The relevant issue was whether the expert
could reliably determine the cause of this tire's separation.

Nor was the basis for Carlson's conclusion simply the
general theory that, in the absence of evidence of abuse, a defect will
normally have caused a tire's separation. Rather, the expert employed
a more specific theory to establish the existence (or absence) of such
abuse. Carlson testified precisely that in the absence of at least two
of four signs of abuse (proportionately greater tread wear on the shoulder;
signs of grooves caused by the beads; discolored sidewalls; marks on the
rim flange) he concludes that a defect caused the separation. And his
analysis depended upon acceptance of a further implicit proposition, namely,
that his visual and tactile inspection could determine that the tire before
him had not been abused despite some evidence of the presence of the very
signs for which he looked (and two punctures).

For another thing, the transcripts of Carlson's depositions
support both the trial court's initial uncertainty and its final conclusion.
Those transcripts cast considerable doubt upon the reliability of both
the explicit theory (about the need for two signs of abuse) and the implicit
proposition (about the significance of visual inspection in this case).
Among other things, the expert could not say whether the tire had
traveled more than 10, or 20, or 30, or 40, or 50 thousand miles, adding
that 6,000 miles was "about how far" he could "say with
any certainty." Id., at 265. The court could reasonably have wondered
about the reliability of a method of visual and tactile inspection sufficiently
precise to ascertain with some certainty the abuse- related significance
of minute shoulder/center relative tread wear differences, but insufficiently
precise to tell "with any certainty" from the tread wear whether
a tire had traveled less than 10,000 or more than 50,000 miles. And these
concerns might have been augmented by Carlson's repeated reliance on the
"subjective[ness]" of his mode of analysis in response to questions
seeking specific information regarding how he could differentiate between
a tire that actually had been overdeflected and a tire that merely looked
as though it had been. Id., at 222, 224-225, 285-286. They would have
been further augmented by the fact that Carlson said he had inspected
the tire itself for the first time the morning of his first deposition,
and then only for a few hours. (His initial conclusions were based on
photographs.) Id., at 180.

*1178 Moreover, prior to his first deposition,
Carlson had issued a signed report in which he concluded that the tire
had "not been ... overloaded or underinflated," not because
of the absence of "two of four" signs of abuse, but simply because
"the rim flange impressions ... were normal." Id., at 335-336.
That report also said that the "tread depth remaining was 3/32 inch,"
id., at 336, though the opposing expert's (apparently undisputed)
measurements indicate that the tread depth taken at various positions
around the tire actually ranged from .5/32 of an inch to 4/32 of an inch,
with the tire apparently showing greater wear along both shoulders than
along the center, id., at 432-433.

Further, in respect to one sign of abuse, bead grooving,
the expert seemed to deny the sufficiency of his own simple visual-inspection
methodology. He testified that most tires have some bead groove pattern,
that where there is reason to suspect an abnormal bead groove he would
ideally "look at a lot of [similar] tires" to know the grooving's
significance, and that he had not looked at many tires similar to the
one at issue. Id., at 212-213, 214, 217.

Finally, the court, after looking for a defense of Carlson's
methodology as applied in these circumstances, found no convincing defense.
Rather, it found (1) that "none" of the Daubert factors, including
that of "general acceptance" in the relevant expert community,
indicated that Carlson's testimony was reliable, 923 F.Supp., at 1521;
(2) that its own analysis "revealed no countervailing factors operating
in favor of admissibility which could outweigh those identified in Daubert,"
App. to Pet. for Cert. 4c; and (3) that the "parties identified no
such factors in their briefs," ibid. For these three reasons taken
together, it concluded that Carlson's testimony was unreliable.

Respondents now argue to us, as they did to the District
Court, that a method of tire failure analysis that employs a visual/tactile
inspection is a reliable method, and they point both to its use by other
experts and to Carlson's long experience working for Michelin as
sufficient indication that that is so. But no one denies that an expert
might draw a conclusion from a set of observations based on extensive
and specialized experience. Nor does anyone deny that, as a general matter,
tire abuse may often be identified by qualified experts through
visual or tactile inspection of the tire. See Affidavit of H.R. Baumgardner
1- 2, cited in Brief for National Academy of Forensic Engineers as Amici
Curiae 16 (Tire engineers rely on visual examination and process of elimination
to analyze experimental test tires). As we said before, supra, at 1977,
the question before the trial court was specific, not general. The trial
court had to decide whether this particular expert had sufficient
specialized knowledge to assist the jurors "in deciding the particular
issues in the case." 4 J. McLaughlin, Weinstein's Federal Evidence
¶ 702.05[1], p. 702-33 (2d ed.1998); see also Advisory Committee's Note
on Proposed Fed. Rule Evid. 702, Preliminary Draft of Proposed Amendments
to the Federal Rules of Civil Procedure and Evidence: Request for Comment
126 (1998) (stressing that district courts must "scrutinize"
whether the "principles and methods" employed by an expert
"have been properly applied to the facts of the case").

The particular issue in this case concerned the use of
Carlson's two- factor test and his related use of visual/tactile inspection
to draw conclusions on the basis of what seemed small observational differences.
We have found no indication in the record that other experts in
the industry use Carlson's two-factor test or that tire experts such
as Carlson normally make the very fine distinctions about, say, the symmetry
of comparatively greater shoulder tread wear that were necessary, on Carlson's
own theory, to support his conclusions. Nor, despite the prevalence of
tire testing, does anyone refer to any articles or papers that validate
Carlson's approach. Compare Bobo, Tire Flaws and Separations, in Mechanics
of Pneumatic Tires 636-637 (S. Clark ed.1981); C. Schnuth et al., Compression
Grooving and Rim Flange Abrasion as Indicators of Over-Deflected Operating
Conditions in Tires, presented to Rubber Division of the American Chemical
Society, Oct. 21-24, 1997; J. Walter & R. Kiminecz, Bead Contact Pressure
Measurements at the Tire- Rim Interface, presented *1179 to Society
of Automotive Engineers, Feb. 24- 28, 1975. Indeed, no one has argued
that Carlson himself, were he still working for Michelin, would have concluded
in a report to his employer that a similar tire was similarly defective
on grounds identical to those upon which he rested his conclusion here.
Of course, Carlson himself claimed that his method was accurate, but,
as we pointed out in Joiner, "nothing in either Daubert or the Federal
Rules of Evidence requires a district court to admit opinion evidence
that is connected to existing data only by the ipse dixit of the expert."
522 U.S., at 146, 118 S.Ct. 512.

Respondents additionally argue that the District Court
too rigidly applied Daubert's criteria. They read its opinion to hold
that a failure to satisfy any one of those criteria automatically renders
expert testimony inadmissible. The District Court's initial opinion
might have been vulnerable to a form of this argument. There, the court,
after rejecting respondents' claim that Carlson's testimony was "exempted
from Daubert-style scrutiny" because it was "technical analysis"
rather than "scientific evidence," simply added that "none
of the four admissibility criteria outlined by the Daubert court are satisfied."
923 F.Supp., at 1522. Subsequently, however, the court granted respondents'
motion for reconsideration. It then explicitly recognized that the relevant
reliability inquiry "should be 'flexible,' " that its "
'overarching subject [should be] ... validity' and reliability,"
and that "Daubert was intended neither to be exhaustive nor to apply
in every case." App. to Pet. for Cert. 4c (quoting Daubert, 509 U.S.,
at 594-595, 113 S.Ct. 2786). And the court ultimately based its decision
upon Carlson's failure to satisfy either Daubert's factors or any other
set of reasonable reliability criteria. In light of the record as developed
by the parties, that conclusion was within the District Court's lawful
discretion.

In sum, Rule 702 grants the district judge the discretionary
authority, reviewable for its abuse, to determine reliability in light
of the particular facts and circumstances of the particular case. The
District Court did not abuse its discretionary authority in this case.
Hence, the judgment of the Court of Appeals is

I join the opinion of the Court, which makes clear that
the discretion it endorses--trial-court discretion in choosing the manner
of testing expert reliability--is not discretion to abandon the
gatekeeping function. I think it worth adding that it is not discretion
to perform the function inadequately. Rather, it is discretion to choose
among reasonable means of excluding expertise that is fausse and science
that is junky. Though, as the Court makes clear today, the Daubert factors
are not holy writ, in a particular case the failure to apply one or another
of them may be unreasonable, and hence an abuse of discretion.

Justice STEVENS, concurring in part and dissenting in
part.

The only question that we granted certiorari to decide
is whether a trial judge "[m]ay ... consider the four factors set
out by this Court in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509
U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), in a Rule 702 analysis
of admissibility of an engineering expert's testimony." Pet.
for Cert. i. That question is fully and correctly answered in Parts I
and II of the Court's opinion, which I join.

Part III answers the quite different question whether
the trial judge abused his discretion when he excluded the testimony of
Dennis Carlson. Because a proper answer to that question requires a study
of the record that can be performed more efficiently by the Court of Appeals
than by the nine Members of this Court, I would remand the case to the
Eleventh Circuit to perform that task. There are, of course, exceptions
to most rules, but I firmly believe that it is neither fair to litigants
nor good practice for this Court to reach out to decide questions not
raised by the certiorari petition. See General Electric Co. v. Joiner,
522 U.S. 136, 150-151, 118 S.Ct. 512, 139 L.Ed.2d 508 (1997) *1180
(STEVENS, J., concurring in part and dissenting in part).

Accordingly, while I do not feel qualified to disagree
with the well-reasoned factual analysis in Part III of the Court's opinion,
I do not join that Part, and I respectfully dissent from the Court's disposition
of the case.